1. Field of the invention
This invention relates to apparatus for sampling bulk granular or powder material, and more particularly to an apparatus for unit dose sampling of mixed bulk material.
2. Description of Related Art
Sampling of bulk mixtures of granular or powdery materials to evaluate the degree of mixing at different locations in a mixing vessel is typically done using a probe or sample thief which is inserted in the bulk mixture to remove a representative sample therefrom. The probes comprise a long tubular shell having at least one aperture on a side wall near the lower end of the probe, and a second inner mating tube also having at least one aperture which can be caused to match the opening in the outer tube by rotating the inner tube within the outer tube. The probe is inserted in the bulk mixture to the desired depth, with the inner tube positioned so that the opening in the inner tube is not aligned with the opening in the outer tube. After insertion of the tube to a desired depth, the inner tube is rotated to align the two openings, allowing bulk material to flow in the opened inner tube. The opening is then closed by again rotating the inner tube, and the probe removed from the bulk material retrieving a sample of the material from a desired point in the mixing vessel. The sample retrieved is recovered from the probe for further analysis or study as needed.
Such bulk sampling apparatus suffers from an inability to sample an accurate and representative sample of the bulk material since there is very little, if any, control of the amount of material that will flow in the probe, so that an accurate and repeatable sample may be obtained and tested.
An improved bulk powder sampling probe, particularly for use in the Pharmaceutical industries where the precise and complete mixing of powdery substances is essential in order to produce uniform content pills, is the SAMPCO Bulk powder Sampler, marketed by the SAMPCO-LANTZ CONSULTANTS of 1 Ripple Court, Keowee Key, Salem, S.C. 29676. This sampler, advertised as a unit sampler uses probes with different capacity sampling chambers, varying in size from 1, 1.5 and 2 cc., providing samples that contain approximately the same amount of powder as corresponds to a single dose of the particular medication, or a small multiple thereof. This apparatus also employs a double tube type arrangement whereby the sampling cavity is filled from the side of the probe, and after filling, is closed for sample retrieval. Thus it is still subject to repeatability errors since filling occurs from the side. In addition, as the sample size decreases, the sampling accuracy further suffers from the difficulty to assure complete recovery of the retrieved sample from the sampling cavity. When the sample is small, any material adhering to the cavity walls becomes a larger proportion of the total sample, introducing variations in the sampled material that may and often do substantially effect the test results. In addition recovery of the powder from the side opening by tapping the probe against the wall of a receiving container results of some powder becoming airborne and lost, as well as some remaining in the cavity, further decreasing the sampling accuracy.
There is thus still a need for an apparatus able to recover predetermined size samples from mixing bulk materials with a high degree of repeatability of the sample size, with minimal disturbance of the bulk material in the sampling vicinity and with the ability to recover substantially all of the retrieved sample from the sampling apparatus in a format easily amenable to further testing.
These and other objects of the present invention will be clear from the following description.